An aluminum electrolytic capacitor is composed of a capacitor element formed by winding an anode foil and a cathode foil through a separator, an electrolyte solution for driving impregnating this capacitor element, a metal case containing this capacitor element, and an elastic sealing member sealing the metal case.
As the electrolyte solution for driving, various electrolyte solutions are used depending on the required performance of the aluminum electrolytic capacitor. In the case of requirement of reliability of aluminum electrolytic capacitor at high temperature and high humidity, the electrolyte for driving having a high electric conductivity and an excellent thermal stability is required. The electrolyte solution used in the aluminum electrolytic capacitor is disclosed in Japanese Laid-open Patent No. 62-264615 and Reopened International Patent Publication No. WO95/15572. Japanese Laid-open Patent No. 62-264615 describes a solvent such as N, N-dimethyl formamide (DMF) or .gamma.-butyrolactone (GBL), a base component of tetralkyl ammonium dissolved in the solvent, and a solute such as quaternary ammonium salt containing carboxylic acid as acid component. Reopened International Patent Publication No. WO95/15572 describes a base component containing alkyl substitute amidine group, and a solute such as amidine salt containing carboxylic acid as acid component.
In order to satisfy the reliability of aluminum electrolytic capacitor by sealing a highly volatile DMF of GBL, as an elastic sealing member, it is known to use crosslinking rubber having a high air tightness and heat resistance. Known examples of such crosslinking rubber include crosslinking rubber having a three-component copolymer of isobutylene, isoprene and divinyl benzene vulcanized by peroxide (IIR-Po) and crosslinking rubber having a copolymer of isobutylene and isoprene vulcanized by using resin as polymer (IIR-Re).
The conventional aluminum electrolytic capacitors has a common problem, that is, the electrolyte solution for driving leaks from around the through-hole of the lead wire of the sealing member. To prevent leak from the through-hole of the lead wire, as disclosed in Japanese Patent Publication No. 8-21527, it is proposed to use, as the elastic sealing member, crosslinking rubber prepared by blending a principal polymer such as three-component copolymer of isobutylene, isoprene and divinyl benzene with at least magnesium oxide, and vulcanizing by peroxide.
In an aluminum electrolytic capacitor using an electrolyte solution for driving containing .gamma.-butyrolactone as solvent and quaternary ammonium salt of organic acid as solute, in the case of electrolytic capacitor comprising a sealing member using this crosslinking rubber blending magnesium oxide, as compared with the aluminum electrolytic capacitor using conventional crosslinking rubber (IIR-Po), leak from around the through-hole of the lead wire of the sealing member at high temperature is improved, but in severe environments of high temperature and high humidity, it is found to have a new problem, that is, the electrolyte solution for driving exudes from around the through-hole of the lead wire of the sealing member.
It is hence an object of the invention to present an aluminum electrolytic capacitor of high reliability free from leak from around the through-hole of the lead wire of the sealing member in severe environments of high temperature and high humidity.